[PATCH 9/9] qspinlock,x86,kvm: Implement KVM support for paravirt qspinlock
From: Peter Zijlstra
Date: Mon Mar 16 2015 - 09:39:31 EST
Implement the paravirt qspinlock for x86-kvm.
We use the regular paravirt call patching to switch between:
native_queue_spin_lock_slowpath() __pv_queue_spin_lock_slowpath()
native_queue_spin_unlock() __pv_queue_spin_unlock()
We use a callee saved call for the unlock function which reduces the
i-cache footprint and allows 'inlining' of SPIN_UNLOCK functions
again.
We further optimize the unlock path by patching the direct call with a
"movb $0,%arg1" if we are indeed using the native unlock code. This
makes the unlock code almost as fast as the !PARAVIRT case.
This significantly lowers the overhead of having
CONFIG_PARAVIRT_SPINLOCKS enabled, even for native code.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/x86/Kconfig | 2 -
arch/x86/include/asm/paravirt.h | 28 ++++++++++++++++++++-
arch/x86/include/asm/paravirt_types.h | 10 +++++++
arch/x86/include/asm/qspinlock.h | 22 ++++++++++++++++-
arch/x86/kernel/kvm.c | 44 ++++++++++++++++++++++++++++++++++
arch/x86/kernel/paravirt-spinlocks.c | 24 +++++++++++++++++-
arch/x86/kernel/paravirt_patch_32.c | 22 +++++++++++++----
arch/x86/kernel/paravirt_patch_64.c | 22 +++++++++++++----
kernel/Kconfig.locks | 2 -
9 files changed, 163 insertions(+), 13 deletions(-)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -692,7 +692,7 @@ config PARAVIRT_DEBUG
config PARAVIRT_SPINLOCKS
bool "Paravirtualization layer for spinlocks"
depends on PARAVIRT && SMP
- select UNINLINE_SPIN_UNLOCK
+ select UNINLINE_SPIN_UNLOCK if !QUEUE_SPINLOCK
---help---
Paravirtualized spinlocks allow a pvops backend to replace the
spinlock implementation with something virtualization-friendly
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -712,6 +712,30 @@ static inline void __set_fixmap(unsigned
#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS)
+#ifdef CONFIG_QUEUE_SPINLOCK
+
+static __always_inline void pv_queue_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+{
+ PVOP_VCALL2(pv_lock_ops.queue_spin_lock_slowpath, lock, val);
+}
+
+static __always_inline void pv_queue_spin_unlock(struct qspinlock *lock)
+{
+ PVOP_VCALLEE1(pv_lock_ops.queue_spin_unlock, lock);
+}
+
+static __always_inline void pv_wait(u8 *ptr, u8 val)
+{
+ PVOP_VCALL2(pv_lock_ops.wait, ptr, val);
+}
+
+static __always_inline void pv_kick(int cpu)
+{
+ PVOP_VCALL1(pv_lock_ops.kick, cpu);
+}
+
+#else /* !CONFIG_QUEUE_SPINLOCK */
+
static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
__ticket_t ticket)
{
@@ -724,7 +748,9 @@ static __always_inline void __ticket_unl
PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
}
-#endif
+#endif /* CONFIG_QUEUE_SPINLOCK */
+
+#endif /* SMP && PARAVIRT_SPINLOCKS */
#ifdef CONFIG_X86_32
#define PV_SAVE_REGS "pushl %ecx; pushl %edx;"
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -333,9 +333,19 @@ struct arch_spinlock;
typedef u16 __ticket_t;
#endif
+struct qspinlock;
+
struct pv_lock_ops {
+#ifdef CONFIG_QUEUE_SPINLOCK
+ void (*queue_spin_lock_slowpath)(struct qspinlock *lock, u32 val);
+ struct paravirt_callee_save queue_spin_unlock;
+
+ void (*wait)(u8 *ptr, u8 val);
+ void (*kick)(int cpu);
+#else /* !CONFIG_QUEUE_SPINLOCK */
struct paravirt_callee_save lock_spinning;
void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
+#endif /* !CONFIG_QUEUE_SPINLOCK */
};
/* This contains all the paravirt structures: we get a convenient
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -3,6 +3,7 @@
#include <asm/cpufeature.h>
#include <asm-generic/qspinlock_types.h>
+#include <asm/paravirt.h>
#define queue_spin_unlock queue_spin_unlock
/**
@@ -11,11 +12,30 @@
*
* An smp_store_release() on the least-significant byte.
*/
-static inline void queue_spin_unlock(struct qspinlock *lock)
+static inline void native_queue_spin_unlock(struct qspinlock *lock)
{
smp_store_release((u8 *)lock, 0);
}
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+extern void native_queue_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+
+static inline void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+{
+ pv_queue_spin_lock_slowpath(lock, val);
+}
+
+static inline void queue_spin_unlock(struct qspinlock *lock)
+{
+ pv_queue_spin_unlock(lock);
+}
+#else
+static inline void queue_spin_unlock(struct qspinlock *lock)
+{
+ native_queue_spin_unlock(lock);
+}
+#endif
+
#define virt_queue_spin_lock virt_queue_spin_lock
static inline bool virt_queue_spin_lock(struct qspinlock *lock)
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -584,6 +584,41 @@ static void kvm_kick_cpu(int cpu)
kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
}
+
+#ifdef CONFIG_QUEUE_SPINLOCK
+
+#include <asm/qspinlock.h>
+
+PV_CALLEE_SAVE_REGS_THUNK(__pv_queue_spin_unlock);
+
+static void kvm_wait(u8 *ptr, u8 val)
+{
+ unsigned long flags;
+
+ if (in_nmi())
+ return;
+
+ local_irq_save(flags);
+
+ if (READ_ONCE(*ptr) != val)
+ goto out;
+
+ /*
+ * halt until it's our turn and kicked. Note that we do safe halt
+ * for irq enabled case to avoid hang when lock info is overwritten
+ * in irq spinlock slowpath and no spurious interrupt occur to save us.
+ */
+ if (arch_irqs_disabled_flags(flags))
+ halt();
+ else
+ safe_halt();
+
+out:
+ local_irq_restore(flags);
+}
+
+#else /* !CONFIG_QUEUE_SPINLOCK */
+
enum kvm_contention_stat {
TAKEN_SLOW,
TAKEN_SLOW_PICKUP,
@@ -817,6 +852,8 @@ static void kvm_unlock_kick(struct arch_
}
}
+#endif /* !CONFIG_QUEUE_SPINLOCK */
+
/*
* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
*/
@@ -828,8 +865,15 @@ void __init kvm_spinlock_init(void)
if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
return;
+#ifdef CONFIG_QUEUE_SPINLOCK
+ pv_lock_ops.queue_spin_lock_slowpath = __pv_queue_spin_lock_slowpath;
+ pv_lock_ops.queue_spin_unlock = PV_CALLEE_SAVE(__pv_queue_spin_unlock);
+ pv_lock_ops.wait = kvm_wait;
+ pv_lock_ops.kick = kvm_kick_cpu;
+#else /* !CONFIG_QUEUE_SPINLOCK */
pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
pv_lock_ops.unlock_kick = kvm_unlock_kick;
+#endif
}
static __init int kvm_spinlock_init_jump(void)
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -8,11 +8,33 @@
#include <asm/paravirt.h>
+#ifdef CONFIG_QUEUE_SPINLOCK
+__visible void __native_queue_spin_unlock(struct qspinlock *lock)
+{
+ native_queue_spin_unlock(lock);
+}
+
+PV_CALLEE_SAVE_REGS_THUNK(__native_queue_spin_unlock);
+
+bool pv_is_native_spin_unlock(void)
+{
+ return pv_lock_ops.queue_spin_unlock.func ==
+ __raw_callee_save___native_queue_spin_unlock;
+}
+#endif
+
struct pv_lock_ops pv_lock_ops = {
#ifdef CONFIG_SMP
+#ifdef CONFIG_QUEUE_SPINLOCK
+ .queue_spin_lock_slowpath = native_queue_spin_lock_slowpath,
+ .queue_spin_unlock = PV_CALLEE_SAVE(__native_queue_spin_unlock),
+ .wait = paravirt_nop,
+ .kick = paravirt_nop,
+#else /* !CONFIG_QUEUE_SPINLOCK */
.lock_spinning = __PV_IS_CALLEE_SAVE(paravirt_nop),
.unlock_kick = paravirt_nop,
-#endif
+#endif /* !CONFIG_QUEUE_SPINLOCK */
+#endif /* SMP */
};
EXPORT_SYMBOL(pv_lock_ops);
--- a/arch/x86/kernel/paravirt_patch_32.c
+++ b/arch/x86/kernel/paravirt_patch_32.c
@@ -12,6 +12,10 @@ DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %c
DEF_NATIVE(pv_cpu_ops, clts, "clts");
DEF_NATIVE(pv_cpu_ops, read_tsc, "rdtsc");
+#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCKS)
+DEF_NATIVE(pv_lock_ops, queue_spin_unlock, "movb $0, (%eax)");
+#endif
+
unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)
{
/* arg in %eax, return in %eax */
@@ -24,6 +28,8 @@ unsigned paravirt_patch_ident_64(void *i
return 0;
}
+extern bool pv_is_native_spin_unlock(void);
+
unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
unsigned long addr, unsigned len)
{
@@ -47,14 +53,22 @@ unsigned native_patch(u8 type, u16 clobb
PATCH_SITE(pv_mmu_ops, write_cr3);
PATCH_SITE(pv_cpu_ops, clts);
PATCH_SITE(pv_cpu_ops, read_tsc);
-
- patch_site:
- ret = paravirt_patch_insns(ibuf, len, start, end);
- break;
+#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCKS)
+ case PARAVIRT_PATCH(pv_lock_ops.queue_spin_unlock):
+ if (pv_is_native_spin_unlock()) {
+ start = start_pv_lock_ops_queue_spin_unlock;
+ end = end_pv_lock_ops_queue_spin_unlock;
+ goto patch_site;
+ }
+#endif
default:
ret = paravirt_patch_default(type, clobbers, ibuf, addr, len);
break;
+
+ patch_site:
+ ret = paravirt_patch_insns(ibuf, len, start, end);
+ break;
}
#undef PATCH_SITE
return ret;
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -21,6 +21,10 @@ DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs")
DEF_NATIVE(, mov32, "mov %edi, %eax");
DEF_NATIVE(, mov64, "mov %rdi, %rax");
+#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK)
+DEF_NATIVE(pv_lock_ops, queue_spin_unlock, "movb $0, (%rdi)");
+#endif
+
unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)
{
return paravirt_patch_insns(insnbuf, len,
@@ -33,6 +37,8 @@ unsigned paravirt_patch_ident_64(void *i
start__mov64, end__mov64);
}
+extern bool pv_is_native_spin_unlock(void);
+
unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
unsigned long addr, unsigned len)
{
@@ -59,14 +65,22 @@ unsigned native_patch(u8 type, u16 clobb
PATCH_SITE(pv_cpu_ops, clts);
PATCH_SITE(pv_mmu_ops, flush_tlb_single);
PATCH_SITE(pv_cpu_ops, wbinvd);
-
- patch_site:
- ret = paravirt_patch_insns(ibuf, len, start, end);
- break;
+#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK)
+ case PARAVIRT_PATCH(pv_lock_ops.queue_spin_unlock):
+ if (pv_is_native_spin_unlock()) {
+ start = start_pv_lock_ops_queue_spin_unlock;
+ end = end_pv_lock_ops_queue_spin_unlock;
+ goto patch_site;
+ }
+#endif
default:
ret = paravirt_patch_default(type, clobbers, ibuf, addr, len);
break;
+
+ patch_site:
+ ret = paravirt_patch_insns(ibuf, len, start, end);
+ break;
}
#undef PATCH_SITE
return ret;
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks
@@ -240,7 +240,7 @@ config ARCH_USE_QUEUE_SPINLOCK
config QUEUE_SPINLOCK
def_bool y if ARCH_USE_QUEUE_SPINLOCK
- depends on SMP && !PARAVIRT_SPINLOCKS
+ depends on SMP
config ARCH_USE_QUEUE_RWLOCK
bool
--
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